Semiconductor fabrication typically involves forming a large number of electrical devices over a substrate. Typically, many of these devices are electrically interconnected with conductive lines. Conductive lines can comprise two or more conductive components such as, for example, titanium nitride (TiN) and polysilicon or a silicide. Such conductive lines are typically formed by blanket depositing conductive material over the substrate and subsequently patterning and etching the conductive material into desired conductive lines.
As device dimensions continue to shrink, etching conductive lines can become problematic due to the undercutting of some of the conductive material from which these lines are formed. For example, FIG. 1 shows a semiconductor wafer fragment generally at 10 which includes a semiconductive substrate 12. In the context of this document, the term "semiconductive substrate" is defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term "substrate" refers to any supporting structure, including, but not limited to, the semiconductive substrates described above. A field oxide region 14 is provided atop which an etched conductive line is disposed generally at 16. Conductive line 16 includes a first conductive material layer 18 and a second conductive material layer 20. Exemplary materials are titanium nitride (first layer 18) and tungsten silicide or polysilicon (second layer 20). These specific materials can be anisotropically etched through the use of an etch chemistry which includes a mixture of NH.sub.4 OH and a peroxide (H.sub.2 O.sub.2). Doing so, however, can cause layer 18 to be undercut such that conductive line 16 does not have substantially vertical sidewalls. Undercutting can be a significant problem as device dimensions shrink and hence, the portion of material removed by the undercut increases in proportion to the total conductive line material. A major factor associated with the undercutting of layer 18 has been found to be a mixture of &lt;111&gt; and &lt;200&gt; grain orientations within the layer.
This invention arose out of concerns associated with providing improved methods of forming conductive structures, and in particular, conductive interconnect lines. This invention also arose out of concerns associated with providing improved semiconductor devices such as memory devices, and specifically, SRAM cells.